Our visual world is filled with clusters (or ensembles) of objects. For many visual tasks, such as attending and selecting specific objects for thoughts or actions, we need to individuate and encode distinctive features from single objects. Such object-specific processing has been the core of cognitive and neuroscientific research for the past few decades. In contrast, there are also ample occasions when our visual system extracts summary statistics from an object ensemble without representing each object in the ensemble in great detail. Such object-ensemble representation can help us rapidly segment an otherwise crowded visual scene and allow us to zoom in on specific objects of interest. Object-ensemble representation thus complements and guides object- specific processing and allows our visual system to overcome the capacity limitation of object-specific processing. Yet despite the common occurrence of object ensembles in our visual world, the cognitive and neural mechanisms underlying object-ensemble processing remains poorly understood. Using fMRI, this proposal will first identify where in the human brain object ensembles are represented, under what attentional condition this representation can be formed, and then examine the nature of the neural object ensemble representation by studying how mean and variance of ensemble features are represented. The proposed studies will be one of the first to systematically investigate how real world object ensembles are processed in the human brain. Besides furthering our understanding of the connection between brain and behavior, results of these studies will have significant impact on current cognitive and neural theories on visual object perception. PUBLIC HEALTH RELEVANCE: The proposed research will help us understand the various constrains and limitations in normal visual cognition. It also has significant implications for understanding the impact of brain damage on visual object perception and recognition.